Heat exchanger flow control



March 19, 1963 G. J. CONSTANTIKES 3,081,823

HEAT EXCHANGER FLOW CONTROL Filed Aug. 21, 1958 FIG. 2

INVENTOR. G.J. CONSTANTIKES VJ y? A TTORNEVS nits;

Ware

Filed Aug. 21, 1958, Ser- No. 756,336 3 Claims. (Cl. 16532) Thisinvention relates to heat exchange systems wherein material flow ismaintained above that at which tube fouling becomes a problem.

When the velocity of a fluid flowing through a heat exchanger is toolow, fouling of the heat exchange surfaces is a problem. This isprimarily due to an increase in the film temperature which causes adeposition of scale on these heat transfer surfaces. This furtherdecreases the heat transfer and greatly reduces the efliciency of theheat exchanger. Flow should be maintained above about 3 feet per secondto prevent excessive fouling of the heat exchange surfaces.

The following are objects of my invention.

An object of my invention is to provide a heat exchange system whereinfouling of heat exchange surfaces is substantially decreased. A furtherobject of my invention is to provide a heat exchange control systemwherein fluid flow is maintained above 3 feet per second. A furtherobject of my invention is to provide an automatic control system whichsenses the rate of flow and automatically adjusts the system to maintainthe desired rate of flow.

Other objects and advantages of my invention will be apparent to oneskilled in the art upon reading this disclosure, which includes adrawing comprising FIGURE 1, a schematic diagram of a heat exchangesystem wherein parallel flow is used when fluid flow is above a certainamount and series flow is used at lower total fluid flow rates;

FIGURE 2, a modification of the invention wherein a portion of the.fluid is returned to the heat exchanger when necessary to maintain thedesired fluid flow rate; and

FIGURE 3, a cross section view of a further modification of my inventionwherein a portion of the heat exchanger is rendered inoperative at lowflow rates so as to maintain the desired rate of flow of fluid materialin the remaining portion of the heat exchanger.

The basic feature of my invention is to provide a system by which flowin the heat exchange system can be maintained above 3 feet per second.Various systems are presented for achieving this result. Broadly, theinvention resides in a heat exchange system comprising at least one heatexchanger containing heat exchange surfaces comprising a plurality oftubes in a shell, means to measure rate of flow of material through atleast one of said tubes and said shell, and means responsive to saidlast-mentioned means to maintain said rate of flow of material incontact with said heat exchange surfaces above a predetermined minimum.

The invention can best be understood by reference to the drawing.

FIGURE 1 illustrates my invention wherein a plurality of heat exchangersare arranged for parallel flow in normal operation but wherein provisionis made for series flow if the fluid material flow rate falls below thedesired rate of 3 feet per second. My invention is applicable toadaption to control of the cooling Water, the material being cooled orboth. In this figure, I have shown control of the flow of cooling water.For ease in explanation, I have shown two heat exchangers 11 and 12. Thecooling tates Patent water is supplied by conduit 13, this conduitsplitting into 7 3,081,823 Patented Mar. 19, 1963 communication withconduit 21 and conduit 22. Conduit 23 extends from heat exchanger 12 toconduit 24 by which the heat exchange liquid is removed from the heatexchange system. The material being cooled is supplied to conduit 26,this conduit communicating with conduit 27 extending to heat exchanger11 and conduit 28 extending to heat exchanger 12. These heat exchangersare, respectively, provided with removal conduits 29 and 31, these beingconnected to removal conduit 32.

Flow controller 33 measures the flow in conduit 18, this flow controllerbeing operatively connected to valves 17 and 19. The system is designedfor division of the cooling fluid and operation of the heat exchangersin parallel. However, when the flow in conduit 18 is below that at whichthe velocity of 3 feet per second is present in the heat exchangers,flow controller 33 closes valve 17 and sets valve 19 so that series flowis obtained. In other words, all of the cooling fluid passes throughconduit 14, heat exchanger 11, conduits 18 and 22, heat exchanger 12,and conduit 24. This results in some sacrifice of total cooling but thisloss in cooling is preferable to fouling of the heat exchange surfaces.

FIGURE 2 illustrates a modification of the invention wherein a recycleline is provided to maintain the desired flow in a heat exchange systemcomprising one or more heat exchangers. More specifically this figureshows heat exchanger 41 provided with inlets 42 and outlet 43. The otherside of the heat exchanger has inlet conduit 44 and outlet conduit 46.The feed supply conduit 47 is connected to pump 48 which pumps intoconduit 44. Conduit 49, provided with valve 51, extends from the outletconduit 46 back to the inlet conduit 47. Flow controller 52 measures theflow in conduit 46, this flow controller being operatively connected tovalve 51.

In the operation of the system of FIGURE 2, there is no flow throughconduit 49 in normal operation. If the amount of fluid material suppliedfalls below that which provides the flow of 3 feet per second in heatexchanger 41, this causes flow controller 52 to open valve 51 and aportion of the liquid is recycled to the heat exchanger. Once again,there is some lowered efliciency because the recycled material haspreviously served as the heat exchange material and is not available forfurther heat exchange.

The invention is also applicable to a single heat exchanger as shown inFIGURE 3. In this: figure the heat exchanger 61 is mounted at a smallangle, a, above the horizontal. The heat exchanger is provided withinlet conduits 62 and 66 and outlet conduits 64 and 63. Within the heatexchanger are a series of valves 67 and 68. While only three valves areshown in the drawing, any desired number can be, of course, used. Flowcontroller 69 is operatively connected to the valves within the heatexchanger and serves to close these valves consecutively as the flow inconduit 64 is reduced. This maintains the flow in the remaining conduitsat or above the desired 3 feet per second. By having the heat exchangerpositioned at a small angle, such as 1 to 10, the tubes so closed drainand fouling is prevented.

Various control systems can be provided to close the valves within theheat exchanger successively. One simple method is to provide a source ofair under pressure and to adjust the various valves so that they areclosed as this pressure increases. Between the valves in the heatexchanger and the source of air pressure there is provided a valveoperated by flow controller 69 and between this valve and valves 67 and68, there is a bleed conduit or orifice. As the flow in conduit 64decreases, this last mentioned valve opens and the air pressure issupplied to valve 67 and/ or valve 68 to close the same.

This invention can be successfully used to regulate flow in the heatexchange system over a considerable range of fluid flow. For instance,removal of supply from a small number of Water pumps would cause a smalldecrease in cooling water and the system could be used to permitcontinued operation Without shutting down operation.

However, if there is a complete breakdown of the cooling tower orcooling Water supply, other measures uld, of course, be necessary.

The invention is illustrated by the following examples which arepresented to provide a complete understanding of the invention.

Example I This example illustrates specific operation when using thesystem of FIGURE 1. The heat exchangers 11 and 12 [are designed so that50 gallons per minute of water passing therethrough gives the desiredrate of flow of 3 feet per second. In operation, 100 gallons per minuteof water are supplied at 90 -F., this water being supplied at a rate of50 gallons per minute to each of the heat exchangers. To these heatexchangers, there is supplied a hot hydrocarbon stream at 240 F. By theheat exchange, the hydrocarbon stream -is cooled in each of the heatexchangers to 105 F. and the water is heated to 110 F.

When the cooling Water supply drops to 90 gallons per minute, it will beseen that the desired rate of flow is no longer possible. When thishappens, flow controller 33 closes valve 17 and adjusts valve 19 so thatthe heat exchangers are connected in series. In heat exchanger 11, thehydrocarbon stream is cooled to 98 F. While the water is heated to 103F., all 90 gallons of water passing through heat exchanger 11 eachminute. This water then passes to heat exchanger 12 Where it is heatedto 114 F. The hydrocarbon stream passing through this second heatexchanger is cooled to 118 F. and the hydrocarbon streams, when mixed,have a temperature of 108 F.

Example II In the operation or" the system of FIGURE 2, the heatexchanger is again designed so that 100 gallons per minute will supplythe desired rate of 110W therein. This water, supplied at 90 F will coolthe hydrocarbon stream from 240 F. to 105 F. When the cooling Water flowdrops to 90 gallons per minute, flow controller 52. opens valve 1s-ufiiciently to provide gallons per minute return flow to conduit 47.This water is heated to 113 F. and recycled through the heat exchangerand, because of this recycle, the hydrocarbon stream is only cooled to109 F. With this recycle, the effiuent from the heat exchange systemrises to the stated' 113 F. instead of the cooler 110 F. when 100gallons per minute of Water are available.

Example 111 In the system of FIGURE 3, the normal operation gives thesame result as Example 11, that is, the 100 gallons per minute of 90 F.Water is heated to 110 F. while cooling the hydrocarbon to 105 F. Whenthe flow drops to 90 gallons per minute, a portion of the tubes areclosed so that all of the heat exchange takes place at the remaining 4heat exchange surfaces. The water is heated to 118 F. and thehydrocarbon cooled to 112 F.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

I claim:

1. A heat exchange system comprising at least one heat exchanger havingan inlet and outlet conduit and containing heat exchange surfacescomprising a plurality of tubes in a shell, means for measuring totalflow of material through said plurality of tubes, means for varying thenumber of heat exchange surfaces available for transfer of heat and howcontrol means operatively connected to said means for varying andresponsive to a signal from said flow measuring means to decrease thenumber of heat exchange surfaces available when said total flowdecreases and vice versa and maintain said rate of flow of materialthrough each of tubes thus remaining open above a predetermined minimum.

2. A heat exchanger comprising a shell containing a plurality of tubes,a first shell inlet conduit, a first shell outlet conduit, a pluralityof valve members within said shell to close individually the inlet endsof said tubes, flow measuring means to determine flow in said outletconduit, 21 flow controller being responsive to a signal from said flowmeasuring means and operatively connected to said valve members toactuate the valve members so as to close a sufficient number of saidtubes when the flow in said outlet conduit decreases and opens moretubes when said flow increases so as to maintain flow through tubes notso closed above a predetermined value.

3. A heat exchanger comprising a shell, a plurality of tubes disposed insaid shell and having inlet and outlet conduits, said tubes beingdisplaced at an angle from the horizontal to permit draining of fluidmaterial therefrom, a shell inlet conduit and a shell outlet conduit incommunication with the above inlet and outlet conduit, a plurality ofvalve members Within said shell to close individually the inlet ends ofsaid tubes, a flow measuring means to determine flow in said shelloutlet conduit, a flow controller operatively connected tosaid valvemembers and responsive toa signal from said flow measuring means toactuate said valve members so as to close a sufiicient number of saidtubes when the flow in said outlet conduit decreases and opens moretubes when said flow increases so as to maintain flow through tubes notso closed above a predetermined value.

References Qited in the file of this patent UNITED STATES PATENTS1,465,171 Parsons et al Aug. 14, 1923 1,465,172 Parsons et al Aug. 14,1923 1,851,765 Henshall Mar. 29, 1932 1,941,365 Patterson et al Dec. 26,1933 2,104,333 Rosenblad Jan. 4, 1938 2,482,261 Goddard Sept. 20, 19492,501,709 Booth Mar. 28, 1950 2,584,211 Kraft Feb. 5, 1952

1. A HEAT EXCHANGE SYSTEM COMPRISING AT LEAST ONE HEAT EXCHANGER HAVINGAN INLET AND OUTLET CONDUIT AND CONTAINING HEAT EXCHANGES SURFACESCOMPRISING A PLURALITY OF TUBES IN A SHELL, MEANS FOR MEASURING TOTALFLOW OF MATERIAL THROUGH SAID PLURALITY OF TUBES, MEANS FOR VARYING THENUMBER OF HEAT EXCHANGE SURFACES AVAILABLE FOR TRANSFER OF HEAT AND FLOWCONTROL MEANS OPERATIVELY CONNECTED TO SAID MEANS FOR VARYING ANDRESPONSIVE TO A SIGNAL FROM SAID FLOW MEASURING MEANS TO DECREASE THENUMBER OF HEAT EXCHANGE SURFACES AVAILABLE WHEN SAID TOTAL FLOWDECREASES AND VICE VERSA AND MAINTAIN SAID RATE OF FLOW OF MATERIALTHROUGH EACH OF TUBES THUS REMAINING OPEN ABOVE A PREDETERMINED MINIMUM.